Arthur Davidsen, 57, Johns Hopkins Astrophysicist, Dies

By DENNIS OVERBYE

Published: July 22, 2001

Correction Appended

Dr. Arthur F. Davidsen, a Johns Hopkins astrophysicist who helped define the density and composition of intergalactic space and was a prime mover in transforming the university into an astronomical powerhouse, died Thursday in a Baltimore hospital. He was 57.

The cause was complications from a lung disorder.

Beginning in 1977, in a series of experiments launched on rockets and then aboard the space shuttle, Dr. Davidsen and his collaborators used the distant and enigmatically powerful cosmic beacons known as quasars as a kind of searchlight shining through millions of light-years of fog to detect traces of the intervening intergalactic matter left from the Big Bang that is thought by many to have started the universe.

He also was acclaimed at Johns Hopkins for leading the drive to bring the Space Telescope Science Institute, the main center for analyzing data from the Hubble Space Telescope, to the campus.

Arthur F. Davidsen was born May 26, 1944, in Freeport, N.Y., on Long Island, the youngest child of Norwegian immigrants. His father was a commercial fisherman and his mother was a housekeeper.

He attended Princeton, where he and some friends created test scores and other credentials for an imaginary person and managed to gain him admission to the university. Mr. Davidsen also found time to play the drums in a rock band.

After he graduated in 1966, he was admitted to graduate school at the University of California, Berkeley, but the Vietnam War intervened. Mr. Davidsen spent five years in the Navy, first as an officer on a destroyer and then at the Naval Research Laboratory.

It was there that he got his taste for space research, working under Dr. Herbert Friedman, a pioneer in sending detectors aloft on rockets to study X-rays, which are blocked by Earth's atmosphere, from the Sun and other energetic cosmic objects.

After receiving his Ph.D. in 1975 and joining Johns Hopkins as an assistant professor, Dr. Davidsen was to make his mark in a similar fashion, by building and launching instruments into space to measure not X-rays but ultraviolet radiation, invisible electromagnetic rays that have shorter wavelengths and higher energies than visible lightwaves.

In 1977 a telescope that he and his team built was launched on an Aerobee rocket, obtaining the first ultraviolet spectrum of a quasar.

That was an especially significant achievement, said Dr. Bruce Margon of the Space Telescope Science Institute, who had known Dr. Davidsen since graduate school. At the time, Dr. Margon said, many astronomers suspected that large quantities of mass, perhaps even enough to eventually reverse the expansion of the universe, might now exist in the form of cool hydrogen lurking in the vast gulfs between the galaxies, where it would absorb some of the ultraviolet light from quasars.

But little such absorption was seen, leading to the conclusion that either the hydrogen (and thus the mass) was not there or that it was in a hot ionized form that did not absorb light.

''He was still just a fuzzy-cheeked assistant professor when he did that,'' added Dr. Margon.

The achievement won Dr. Davidsen the American Astronomical Association's Helen B. Warner Prize for outstanding research performed by an astronomer under the age of 36.

He followed up by building a larger telescope, the Hopkins Ultraviolet Telescope, known as HUT, to study quasars, galaxies, hot stars and solar system objects. It was designed to fly on the space shuttle as part of a package called Astro, but it was delayed by the explosion of the Challenger in 1986. The telescope's first flight, known as Astro-1, in 1990, was only partially successful, because of technical glitches.

The package was flown again as Astro-2 in 1995 on a 16-day mission that Dr. Davidsen called ''an unqualified scientific success.'' Among other things, HUT's measurements and Dr. Davidsen's subsequent analyses helped show that the intergalactic gas from which galaxies condensed is not uniform but ''a diverse tapestry of variations,'' Dr. Margon said.

Back on Earth, Dr. Davidsen was also having an effect. NASA had put out a call in the late 1970's for proposals to be the host for a scientific institute that would operate its space telescope, the grandest thing happening in astronomy.

The plum was widely regarded as destined for Princeton, home of Dr. Lyman Spitzer, who had come up with the idea of a space telescope. Dr. Davidsen argued, however, that Johns Hopkins had a chance, and he prevailed on the university to submit a proposal to the Association of Universities for Research in Astronomy, which operates observatories in Arizona, Hawaii and Chile, among other places.

Dr. Davidsen was unfazed by the long odds. When the selection committee visited the campus in Baltimore, recalled Dr. Stuart Bowyer, one of Dr. Davidsen's professor at Berkeley, Dr. Davidsen had assembled 50 mayors from surrounding communities to offer their support for the project. ''Who would have thought of that?'' Dr. Bowyer asked.

The announcement that Johns Hopkins had won put the school at the center of the astronomical universe. ''It changed the face of physics and astronomy at Hopkins and made it into an astrophysics powerhouse,'' said Dr. Paul Feldman, chairman of the physics and astronomy department.

Dr. Davidsen was also the founding director of the Center for Astrophysical Sciences, which helps organize large astronomical projects at Johns Hopkins.

He also was interim dean of the Krieger School of Arts and Sciences. At his death he was chairman of the advisory council for the Sloan Digital Sky Survey, a multi-institutional project to map the universe.

On Friday, Dr. Davidsen, a professor of physics and astronomy, was being remembered as a mulitfaceted person, a musician who could pick up a guitar and lead a crowd through two hours of doo-wop singing and who led high school expeditions to jazz clubs in Manhattan, a fly fisherman and a lover of his Harley-Davidson Fatboy.

He is survived by his wife, Krauke Davidsen; two sons, Andrew and Austin; two stepsons, Nick and Jesse Tischler; and a sister, Sylvia Klecak. His marriage to Anita Clare Saltz ended in divorce.

Dr. Davidsen had long hoped for a third flight for HUT. Although that was not to be, he was pleased this year when the telescope was sent to the Smithsonian's National Air and Space Museum to be part of a major exhibit opening this fall.

The Johns Hopkins Magazine reported that Dr. Davidsen told one of his sons, a college freshman, that HUT was going to the museum. ''He said going there was much cooler than going into orbit one more time,'' Dr. Davidsen told the magazine. ''I can't go that far myself but I certainly am thrilled and pleased because it validates the importance of the project.''

Photo: Dr. Arthur F. Davidsen, a professor of astronomy at Johns Hopkins. (Marty Katz for The New York Times)

Correction: July 24, 2001, Tuesday An obituary on Sunday about Dr. Arthur F. Davidsen, an astrophysicist at Johns Hopkins University, misspelled the given name of his wife. She is Frauke Davidsen, not Krauke.